1. Technical Field
The present invention relates to a vibrator element, a vibrator, a vibration device, an electronic apparatus, and a frequency adjustment method.
2. Related Art
As the vibration device such as a quartz crystal oscillator, there is known a device provided with a tuning-fork vibrator element having a plurality of vibrating arms (see, e.g., JP-A-2009-5022 (Document 1)).
For example, the vibrator element described in Document 1 has a base section, three vibrating arms extending from the base section in parallel to each other, and a piezoelectric element composed of a lower electrode film, a piezoelectric film, and an upper electrode film formed on each of the vibrating arms in this order. In such a vibrator element, each of the piezoelectric elements is provided with an electrical field applied between the lower electrode film and the upper electrode film, thereby making the piezoelectric layer compress, and causing the flexural vibration in the vibrating arms in a direction (so-called an out-of-plane direction) of the thickness of the base section.
In such a vibrator element, in general, a metal film is provided on the tip portion of each of the vibrating arms, and the metal film is partially removed by laser irradiation, thereby performing the adjustment of the frequency (the resonant frequency) of the flexural vibration of the vibrating arms (see, e.g., JP-A-2008-160824 (Document 2)).
For example, according to the frequency adjustment method described in Document 2, metal films for adjusting the frequency are formed on respective plate surfaces of the vibrating arms each having a plate-like shape so as to have the same patterns. Then, by irradiation with the laser beam, a part of the metal film on one of the plate surfaces of the vibrating arm and a part of the metal film on the other of the plate surfaces are removed simultaneously to thereby perform coarse adjustment, and then, by irradiation with the argon ion beam, a part of the one of the plate surfaces of the vibrating arm is further removed to thereby perform fine adjustment.
However, according to the frequency adjustment method described in Document 2, since the metal film on the one of the plate surfaces of the vibrating arm and the metal film on the other of the plate surfaces have the same patterns, the metal film on the one of the plate surfaces of the vibrating arm and the other of the plate surfaces are removed simultaneously by irradiation with the laser beam. Therefore, there arises a problem that it is difficult to separately remove a part of the metal film on the one of the plate surfaces of the vibrating arm and a part of the metal film on the other of the plate surfaces by irradiation with the laser beam, and therefore, the fine adjustment of the frequency is difficult.
Incidentally, the frequency “f” of the flexural vibrator is given as f≈t/L2 (“t” denotes the thickness of the vibrating arm in the vibration direction, “L” denotes the length of the vibrating arm in the extending direction), and in the case of achieving downsizing of the vibrator having the vibrating arm perform flexural vibration in the out-of-plane direction as described in Document 1 mentioned above, if the length L of the vibrating arm is reduced, it is required to reduce the thickness “t” of the vibrating arm in the vibration direction (the thickness direction of the vibrating arm) of the vibrating arm in accordance with the reduction in the length L. Specifically, since the thickness of the vibrating arm in the vibration direction is as considerably small as several micrometers, it is easy for the laser beam emitted from one side of the vibrating arm to reach the other side of the vibrating arm. Further, since the smaller the thickness of the vibrating arm is, the larger the variation (the amount of rise) in the frequency with respect to the mass (the mass to be reduced) of the metal film to be removed becomes, the fine adjustment of the frequency becomes difficult. In contrast, in the typical vibrator element having the vibrating arm perform the flexural vibration in a plane having the normal line in the thickness direction of the base section, the thickness “t” of the vibrating arm in the vibration direction corresponds to the width direction of the vibrating arm. Therefore, since there is no need for forming the vibrating arm as a thinner plate, the problem described above does not arise. According to such circumstances as described above, if such a frequency adjustment method as described above is used in the vibrator element having the vibrating arm perform the flexural vibration in the out-of-plane direction, the problem that the metal films on the both surfaces are removed by the laser penetrating the vibrating arm when adjusting the frequency, thereby shifting the frequency from the target frequency becomes prominent.